Abstract Homeless adults are at high risk for Hepatitis B virus (HBV), Hepatitis C virus (HCV) and HIV infection due to high rates of injection drug use and unprotected sexual activity. Our NIDA-funded RO1 award has enabled us to implement a successful intervention designed to evaluate the effectiveness of a HBV vaccination intervention with homeless adults. Our findings revealed that a greater percent of homeless adults randomized to the Nurse Case Managed Plus Incentive and Tracking group completed the HAV/HBV vaccine series compared to a Standard program without tracking. Homeless persons least likely to complete the vaccine series were young (< 40), and were men having sex with men (MSM); a significant number of these young adults also reported methamphetamine (MA) and cocaine/crack use. Stimulants (SAs), including MA and cocaine/crack are commonly used by homeless MSM, who contend with disorganized lives, unemployment, and little access to health and social services; thus, HBV vaccination is particularly challenging in this population. HAV/HBV vaccination and effective behavioral treatment are two of the most important strategies for reducing HBV infection among this at-risk group of SA users. Based upon advice from our community partners who have successfully treated SA-using gay and bisexual men (GBM), we will incorporate contingency management into our vaccination completion program, which had lower completion rates among young adults and MSMs. Thus, in thiscompetitiverenewal,we propose a randomized, experimental, two-group design to evaluate the effectiveness of a Nurse Case Managed Program, which includes specialized education and Contingency Management and Tracking (NCCMT), with a Standard Program, including brief education, Contingency Management and Tracking (SCMT) with 500 homeless, young (18-39), SA-using GBM,oncompletionof theTwinrixHAV/HBV vaccine and, secondarily, on reduction of risk for hepatitis and HIV. This study is innovative in that it will allow us to look at the effect of an enhanced case management and contingency management program versus a standard contingency management program. The proposed study combines optimal strategies to approach, engage and intervene with a hidden and high- risk population to assess the feasibility and efficacy of interventions that may prove beneficial in preventing HBV and HAV infections. We will also assess the relative cost of these programs in terms of completion of the HAV/HBV vaccination series. As use of SAs threatens to intensify homeless persons' risk of exposure to HAV and HBV, particularly among young users who may not yet be HBV-infected, research targeted to engage this group in treatment, until they are suitably protected from HBV, is critical.